1. Field of the Invention
The present invention relates to an inter-axle differential, and more particularly, to an improved locking clutch for inter-axle differentials.
2. Discussion of Related Art
A conventional tandem axle assembly for heavy-duty trucks used in on-road and off-road service includes forward and rear axle assemblies and an intermediate drive shaft assembly connecting the two axle assemblies. The forward and rear axle assemblies each include a pair of axle half shafts extending therefrom on which one or more wheels of a vehicle are mounted. The axle half shafts in each axle assembly are driven by a wheel differential. The wheel differential includes a pinion gear in mesh with a ring gear (which in turn drives a plurality of bevel gears to cause rotation of the axle half shafts).
Tandem axle assemblies commonly employ an inter-axle differential to divide power between the forward and rear axle assemblies. The inter-axle differential enables speed differences between the drive axles, e.g., to allow torque balance between the drive axles during the vehicle cornering, to compensate for tire size differences, etc.
The inter-axle differential is generally housed within the forward axle assembly. The inter-axle differential for a conventional tandem axle assembly typically includes an input shaft extending into a housing of the forward axle assembly and a spider (or cross-member) mounted on the input shaft and supporting a plurality of bevel pinion gears. The inter-axle differential further includes a pair of side gears in mesh with, and driven by, the pinion bevel gears. One side gear is used to drive the pinion gear of the forward axle assembly wheel differential. The other side gear is coupled to an output shaft that extends outwardly from the forward axle assembly housing and drives the intermediate drive shaft assembly and, indirectly, the pinion gear of the rear axle assembly wheel differential.
At times, it may be necessary to lock the inter-axle differential. For example, during hazardous driving conditions it may be necessary to prevent power from being delivered to a wheel that has lost traction. In conventional inter-axle differentials, a locking clutch member is disposed about the input shaft and can be shifted into engagement with a second clutch member typically defined by one of the side gears to lock the inter-axle differential. Shifting of the locking clutch member is typically accomplished using a shift fork that is received within the clutch member and is moved through mechanical or electronic actuation. In particular, a piston may urge a pushrod against the shift fork.
Conventional locking clutches for inter-axle differentials have several drawbacks. First, the pushrod and piston are commonly located at a radial distance from the clutch members thereby consuming valuable space and material in the axle assembly housing. Second, tooling for the piston, pushrod and shift fork are relatively expensive, and production of these components is also relatively expensive. Third, relative rotation occurs between the shift fork and clutch member that causes wear on the shift fork. Fourth, the tendency to place the piston and pushrod bores in separate parts creates misalignment concerns. Finally, the offset load applied to the shift fork by the pushrod causes the shift fork to tip, increasing wear on the fork and clutch member and potentially resulting in binding of the clutch splines.
The inventors herein have recognized a need for a clutch for an inter-axle differential that will minimize and/or eliminate the above-identified deficiencies.